1. Field of the Invention
This invention relates to overbased alkali metal sulfonates and lubricating oil compositions containing said sulfonates. More particularly, it relates to carbonate overbased alkali metal sulfonates that are prepared in a unique manner which minimizes formation of a hazy product.
2. Description of the Prior Art
The use of the normal salts of petroleum sulfonic acids as additives for lubricating oil compositions is well known. During World War II, normal metal sulfonates that were derived from mahogany or petroleum sulfonic acids were employed as detergent additives in internal combustion engine crankcase oils. Calcium or barium was employed as the metal in such sulfonates. Subsequently, sulfonate products which contained as much as twice as much metal as the corresponding normal or neutral metal sulfonate were found to have improved detergent power and ability to neutralize acidic contaminants and, hence, were used in the place of the normal sulfonates. More recently, fully oil-soluble sulfonates containing from 3 up to 20 or more times as much metal as a corresponding normal metal sulfonate have been developed. These highly basic sulfonates have been identified as "overbased," "superbased," and "hyperbased."
Over the years, numerous methods for preparing overbased sulfonates have been disclosed. In general, such overbased sulfonates have been prepared by mixing a promoter and a solvent with a normal sulfonate and an excessive amount of a metallic base of either an alkali metal or an alkaline earth metal, heating the resulting mixture, carbonating the resulting reaction mass with sufficient carbon dioxide to increase the amount of metal base colloidally dispersed as metal carbonate in the resulting product, and then filtering the resulting material.
In U.S. Pat. No. 3,488,284, LeSuer, et al. disclosed the preparation of basic metal complexes wherein a mixture of an oil-soluble organic acid compound, such as a sulfonic acid, a basically reacting metal compound, such as sodium hydroxide, and an alcoholic promoter having from one to four hydroxyl groups, such as methanol, are treated with an inorganic acidic material, such as carbon dioxide, to form the desired basic metal complex and subsequently the volatile materials, primarily the alcoholic promoter, are stripped from the product mass. They disclosed further that, during the step that the mixture is treated with the inorganic acidic material, the mixture must contain substantially no free water and, if water is liberated during this step, such as the water of hydration in the basically reacting metal compound, reaction conditions should be such that substantially all of such liberated water is driven off as it is formed.
In West German Patent No. 1,122,526, Groot disclosed a method for the preparation of an alkali metal salt of an organic carboxylic acid or an organic sulfonic acid having a high degree of basicity. According to this patent, the oil-soluble basic alkali metal salt of organic sulfonic acids or carboxylic acids is prepared by the method which comprises reacting the alkali salt of the organic acid dissolved in hydrocarbon oil, in the presence of water, and/or of an oxygen-containing organic solvent which is miscible with water, with the carbonate of an alkali metal, which is formed conveniently in the reaction mixture itself. The organic solvent can be selected from aliphatic alcohols, such as methanol, ethanol, propanol, isopropanol, normal-butanol, and isobutanol. The carbonate of a particular alkali metal can be formed in situ by the addition of the hydroxide of the alkali metal to the reaction mixture and the subsequent passage of carbon dioxide through the reaction mixture. While this West German patent disclosed that temperatures between 20.degree. C. (68.degree. F.) and 150.degree. C. (302.degree. F.), especially between 40.degree. C. (104.degree. F.) and 120.degree. C. (248.degree. F.), are suitable, the patent disclosed that the process should be carried out at a temperature that preferably does not exceed the boiling point of the lowest boiling reactant in the reaction mixture. It then disclosed that the reaction mixture can be dried by heating to temperatures of 135.degree. C. (275.degree. F.) to 160.degree. C. (320.degree. F.). In each of the examples, the temperature during the addition of the carbon dioxide to the reaction mixture was kept well below 100.degree. C. (212.degree. F.).
In United Kingdom Patent Specification No. 1,481,553, King disclosed a process for the preparation of a stable oil-soluble dispersion of a basic alkali metal sulfonate having a metal ratio of at least 4, wherein an acidic gaseous material selected from carbon dioxide, hydrogen sulfide, sulfur dioxide, and mixtures thereof was contacted with a reaction mixture comprising one or more oil-soluble sulfonic acids or derivatives thereof, one or more alkali metals, alkali metal hydrides, or basically reacting alkali metal compounds, one or more lower aliphatic alcohols, and one or more oil-soluble carboxylic acids or derivatives thereof for a period of time that was sufficient for the acidic gaseous material and the components of the reaction mixture to form a dispersion of basic alkali sulfonate having the desired metal ratio. The reaction was carried out at a temperature within the range of 25.degree. C. (77.degree. F.) to 200.degree. C. (392.degree. F.).
In U.S. Pat. No. 4,326,972, Chamberlin disclosed the preparation and use of an oil-dispersible basic alkali metal sulfonate. In the preparation, a reaction mixture comprising at least one oil-soluble sulfonic acid or derivative thereof, at least one alkali metal or basic alkali metal compound, at least one lower aliphatic alcohol, and at least one oil-soluble carboxylic acid or functional derivative thereof is reacted with at least one acidic gaseous material selected from the group consisting of carbon dioxide, hydrogen sulfide, sulfur dioxide, and mixtures thereof. Chamberlin disclosed that the reaction temperature was not critical and that it would be between the solidification temperature of the reaction mixture and its decomposition temperature, i.e., the lowest decomposition temperature of any component of the mixture. He indicated that usually the temperature would be from about 25.degree. C. (77.degree. F.) to about 200.degree. C. (392.degree. F.), preferably from about 50.degree. C. (122.degree. F.) to about 150.degree. C. (302.degree. F.). In an example, carbon dioxide flow was utilized while the temperature was less than 100.degree. C. (212.degree. F.).
There has now been found a method for preparing a superior carbonate overbased alkali metal sulfonate. This overbased sulfonate is an extremely clear product. It has a very high base number, is oil soluble, and is low in viscosity.